Interpretive Summary: Nitrate emanating from artificial subsurface drains in the U.S. Midwest has been implicated as a strong contributing factor to water quality problems such as hypoxia in the Gulf of Mexico. Balancing the amount of N needed for optimum plant growth while minimizing nitrate transport to ground and surface waters, however, remains a challenge. Field studies are limited that investigate the water quality effects of multiple management practices such as nitrogen application timing and amount. Agricultural simulation models may be one method to cost-effectively investigate the effect of a variety of management practices under a variety of conditions. The Root Zone Water Quality Model (RZWQM) was calibrated to long-term (1990-2003) data near Nashua, Iowa, which includes 36 plots with a variety of crop rotations, tillage, and manure and fertilizer applications. The model adequately responds to year-to-year climate variation and to plot-to-plot management variation within a year. The calibrated model will be used to populate a database that quantifies the water quality and yield effect of multiple agricultural management practices under several climate and soil conditions. A database such as this may be a useful tool that simply and objectively quantifies the tradeoffs of management alternatives, which may help accelerate adoption of best management practices.

Technical Abstract:
Nitrate emanating from artificial subsurface drains in the U.S. Midwest has been implicated as a strong contributing factor to water quality problems such as hypoxia in the Gulf of Mexico. Balancing the amount of N needed for optimum plant growth while minimizing nitrate transport to ground and surface waters, however, remains a challenge. Field studies are limited that investigate the water quality effects of multiple management practices such as nitrogen application timing and amount. Agricultural simulation models may be one method to cost-effectively investigate the effect of a variety of management practices under a variety of conditions. The Root Zone Water Quality Model (RZWQM) was calibrated to long-term (1990-2003) data near Nashua, Iowa, which includes 36 plots with a variety of crop rotations, tillage, and manure and fertilizer applications. The model adequately responds to year-to-year climate variation and to plot-to-plot management variation within a year. The calibrated model will be used to populate a database that quantifies the water quality and yield effect of multiple agricultural management practices under several climate and soil conditions. A database such as this may be a useful tool that simply and objectively quantifies the tradeoffs of management alternatives, which may help accelerate adoption of best management practices.